1. Field of the Invention
This invention relates generally to food or edible materials and especially to a process for preparing an emulsion based food salad with improved low temperature properties.
In particular, this invention concerns a method for inhibiting physical change in an emulsion by contact with a chemical agent.
2. Background of the Invention
Emulsions are dispersions of one liquid in another with one of the liquids being water or an aqueous solution and the other liquid being an oil or water-immiscible liquid. Mayonnaise and mayonnaise-like emulsified dressings are comprised of oil-in-water emulsions. A problem with oil-in-water emulsions is lack of physical stability under low temperature conditions. During freezing ice crystals are formed within dispersed water droplets forcing the droplets closer together and inducing rupture of a thin film between the droplets. This causes the droplets to flow together and coalesce upon thawing. Protein-stabilized emulsions and emulsions having ionic surfactants tend to provide more resistance to coalescence however under extreme temperature conditions these inhibitors may not be effective, probably due in part to the physical changes brought about by interfacial rheology phenomena including dilation and shear which deform the droplets resulting in instability. Consequently, there is a breakdown of the emulsion and an undesirable separation of the oil from the water droplets upon thawing.
Emulsion based food salads commonly have a limited shelf-life and therefore are generally regionally produced for local non-frozen distribution. The ability to prepare a freezably stable emulsion based food salad is fundamental for accessing national and international markets. Frozen-phase salad distribution would thus provide economic benefits particularly in the commercial and institutional food service industry. The long-term storage advantages of frozen salad products would also expand production planning options, for example, larger manufacturing runs could be possible with excess product being frozen-preserved; manufacturing could be scheduled when ingredients are accessible and/or are in season and less expensive; and food processing could be scheduled when there is plant downtime with the product subsequently being frozen-stored to meet future supply demands. The process of this invention also opens opportunities for new products such as frozen salad sandwiches that are microwave stable.
Previous attempts to prepare freeze-thaw salad dressings include a process that utilizes a cooked starch base, as disclosed in U.S. Pat. No. 3,676,157. Another process, shown in U.S. Pat. No. 4,423,084, also requires cooked starch. A limitation of the previous processes is that they rely upon a starch base. Furthermore, the dressings described in the above patents are not intended for use in the manufacture of emulsion based food salads. Another shortcoming is that these processes are not effective for emulsions having a high fat content as in the present invention. A further limitation of the previously described processes is the lack of melt point control during the thawing stage. The prior processes further lack integrated microbial maintenance.